Transition Subnet Create command in config-agents doc
Transition Subnet Create command in config-agents doc

OSC has implemented subnet create ipv6 options.
Need to transition docs to reflect the OSC transition.

Partially Implements: blueprint use-openstack-command

Change-Id: Id2d38181450010e0cbd0e40240c4de5e9d16d8f3

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals